1. Field of the Invention
This invention generally relates to a coating having a primer layer that includes at least one elastic polymer.
2. Description of the Background
Stents are used not only as a mechanical intervention of vascular conditions but also as a vehicle for providing biological therapy. As a mechanical intervention, stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically, stents are capable of being compressed, so that they can be inserted through small vessels via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in patent literature disclosing stents which have been applied in PTCA (Percutaneous Transluminal Coronary Angioplasty) procedures include stents illustrated in U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor. Polymeric coatings have been used for local delivery therapeutic substances to a leision site via, e.g., stenting. A polymer with groups compatible with the surface of a medical device, e.g., ester group, will have a good adhesion when coated on top of the device. When a polymer has a right glass transition temperature (Tg), right molecular weight, it can used to form a primer layer for a coating. However, even one uses a polymer layer with good adhesion to the surface of a device, delamination or cracking can occur upon deploying the device, e.g., stent expansion.
The embodiments of the present invention provide for methods addressing these issues.